Cathode-ray tube for image reproduction



Nov. 12, 1957 A. cs. VAN DOORN 2,813,214

CATHODE-RAY TUBE FOR IMAGE REPRODUCTION Filed Jan. 5, 1955 ADRIAAN GERARD VAN DOORN v f a I INVENTOR AGENT United States Patent CATHODE-RAY TUBE FOR IMAGE REPRODUCTION Adriaan Gerard van Doorn, Emmasingel, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application January 5, 1955, Serial No. 479,939

Claims priority, application Netherlands February 23, 1954 6 Claims. (Cl. 313-78) The invention relates to a cathode-ray tube, more particularly for the reproduction of coloured television images, the tube comprising acollecting screen, on which an image is drawn, and two grids arranged at a small distance from this screen.

For various purposes cathode-ray tubes have been constructed, which comprise a collecting screen, for example a luminescent screen, on which an image is drawn, these tubes comprising in front of this screen, i. e. on the cathode side thereof, two grids which lie practically in one plane and which have exclusively parallel wires lying in this plane in a manner such that the wires of the two grids alternate with one another. Such tubes have been particularly constructed for use in devices for the reproduction of coloured television images. With the aid of such grids t the image may have a line structure and by a suitable construction of the luminescent screen, for example with alternating strips of materials luminescing in different colours, a colour image may be reproduced. Such tubes have furthermore been suggested for the reproduction of stereoscopic images. For many uses it is necessary to apply high voltages between the two grids, these voltages having values varying between a few hundreds and a few thousands of volts. In order to collect few electrons and to obtain a sharply defined image, very thin wires are used for these grids. These thin wires and the high voltage differences between the two grids give rise to a serious disadvantage. With variation of the voltage between the two grids considerable electrostatic forces are produced be tween the grid wires. The wires of a grid lying between two wires of the other grid are subjected on both sides to the same forces, provided that the distances between the wires are equal on both sides, which is usually the case. There is, however, a difiiculty with the extreme wires, i. e. the wires lying on the grid sides. If no particular precautions are taken, these wires are in general subjected to a force on one side, i. e. on the side directed towards the centre of the grid.

The invention has for its object to provide the same condition for the two extreme wires as for the further wires of the grids.

A cathode-ray tube according to the invention, more particularly a tube for the reproduction of coloured television images, comprises a collecting screen, on which an image is drawn and two grids located at a small distance in front thereof, and having exclusively parallel, thin wires lying in a plane substantially parallel to the collecting screen, in a manner such that the wires of the grids alternate with one another, and is characterised in that parallel to each extreme grid wire, spaced apart therefrom by a distance equal to the distance between this Wire and the adjacent wire, provision is made of a rigid, conductive part lying substantially in the plane of the grids and connected electrically to the last-mentioned wire.

Owing to the construction in accordance with the invention, the extreme thin wires of the grids lie between two conductive parts which are always at the same potential.

At a variation of the voltage between the two grids, the same forces are thus exerted on each extreme wire on either side thereof. The wires are thus prevented from moving towards one another and from producing even a short-circuit between the two grids.

The rigid, conductive part may, for example, be a grid wire of a thickness such that it is no longer liable to bend. As an alternative, a conductive strip for example of metal may be used. This strip may for example be at right angles to the plane of the grids. According to a particular aspect of a tube according to the invention, the rigid, conductive part is constituted by the side of a frame, on which the grid wires of one grid are mounted.

Where reference is made above and hereinafter to thin grid wires, this is to be understood to mean that the diameter of these wires lies between 25 and 25 0a. For normal television tubes for the reproduction of colour images the space between the centre line of the grid wires is, in general 0.5 mm.

It is, of course, not necessary for the two extreme wires to be associated with the same grid and to be, consequently, at the same potential. If this is the case, a very simple construction may be obtained, in which the wires of one grid are wound on a frame and the sides of this frame constitute the rigid, conductive parts, as referred to above.

The invention will now be described more fully with reference to a drawing, in which- Fig. 1 shows diagrammatically the construction of a cathode-ray tube according to the invention and Figs. 2, 3, 4, 5 and 6 show more in detail the relative positions of the grids, the grid wires and the aforesaid rigid, conductive parts.

According to Fig. 1, the envelope of the cathode-ray tube is constituted by a cylindrical part 1 and a conical part 2, secured thereto and sealed by a substantially flat window 3. Reference numeral 4 designates the electron gun, and numerals 5 and 6 designate a focusing coil and a deflection coil system respectively. On the window 3 provision is made of a luminescent screen 7, in front of which two grids 8 and 9 are arranged, the wires of which lie in one plane which is substantially parallel to the surface 7 and alternate with one another.

Fig. 2 shows the course of the grid wires and their connection in a tube as shown in Fig. 1. In this case the grids are secured to conductive strips 10 and 11, 12 and 13 respectively. During the operation of the tube a high voltage, which is variable, is applied between these strips and hence between the grid wires. At this variation electro-static forces are exerted on the wires secured to the strips 10 and 12 owing to the provision of the wires secured to the strips 11 and 13. It is evident that the wires secured to the strips 10 and 12 will not deviate in the plane of the grids, since they are flanked on either side by the wires secured to the strips 11 and 13. The same applies to the wires 15, 16 and 17, secured to the strips 11 and 13. However, if the wires 18 and 19 would be flanked only on one side by a wire secured to the strips 10 and 12, a force directed to the centre of the grid would be exerted thereon. This would give rise to a tendency of the wires to move to the centre owing to their low rigidity and to touch the adjacent wires, so that they could produce a temporary or even permanent short-circuit between the grids. At the side of the extreme wires 18 and 19, however, provision is made of thick wires 20 and 21 respectively, which are secured to the strips 10 and 12. Consequently, also the extreme wires are thus located between two parts which are always at the same potential during the operation of the tube. The space between the wires 18 and 20 and between 19 and 21 respectively is chosen to be equal to the space between the wires 18 and 19 and the adjacent thin wires, secured to the strips 10 and 12.

With the embodiment shown in Fig. 2, provisions are of course, taken that the wires secured to the strips 10 and 12 do not contact with the strips 11 and 13. This may for example be obtained by coating these wires with an insulating layer at the'ar'ea where they pass by these strips.

Fig. 3 shows a slightly modified construction, in which the wires of one grid are mounted on a frame 22. From the sectional view of this construction shown in Fig. 4 it is evident that the side of the frame 22 constitutes the rigid, conductive part, as referred to above.

In order to re-inforce the frame and to improve the centring of the extreme wires in the electric field, the frame may for example be provided with upright edges on the sides flanking the grid Wires. Such an embodiment is shown diagrammatically in Fig. 5, in which the frame is designated by 23, the upright edges by 24 and 25.

Fig. 6 shows a further construction of the grid system, in which the two extreme wires do not belong to the same grid. The wires of one grid are secured on the one hand to the straight strip 27 and on the other hand to a strip 28 bent at right angles. The wires of the other grid are secured to a straight strip 29 and a bent strip 30. Also in this construction the extreme wires 31 and 32 are flanked by a grid wire and part of the strips bent at right angles, which are at the same potential during operation as the wires 33 and 34. Thus the wires 31 and 32 are prevented from bending.

What is claimed is:

1. In a cathode-ray tube including a screen for producing color television images, said tube including a pair of electrically-separated grids located in front of the screen and each comprising electrically-connected, parallel, thin wires subject to movement when exposed to an electrostatic field and all of the wires of both grids lying substantially in one plane, the wires of said pair of grids being alternately arranged so that each wire of one grid lies between wires of the other grid, except for the two grid wires at the. opposite ends of the grids, and is spaced therefrom a given distance, the improvement comprising the provision of rigid, substantially immovable, conductive members mounted parallel and adjacent to said two grid wires at the opposite ends and on the side thereof remote from the other grid wires, said conductive members lyingsubstantially in the same plane as the grid wires and being spaced from the end grid wires a distance substantially the same as said given distance, each of said conductive members being electrically connected to the grid wire adjacent said grid wire at the end of the grid, whereby said end grid wires are subjected to substantially the same electrostatic field from opposite sides when different potentials are applied to the different grids and are thus prevented from undergoing appreciable movement.

2. A cathode-ray tube as set forthin claim 1 wherein one of the grids comprises a rigid, conductive frame member to which are secured its grid wires, the end wires of the other grid lying between a side of the frame member and the adjacent grid wire.

3. A cathode-ray tube as set forth in claim 1 wherein the wires of each of the grids are mounted on separate frame members, the rigid, substantially immovable, conductive members constituting thick wires mounted on opposite ends of one of the frame members.

4. A cathode-ray tube as set forth in claim 1 wherein the rigid, conductive members include a fiat, strip-like portion extending at right angles to the plane of the grid.

5. A cathode-ray tube as set forth in claim 1 wherein the rigid, conductive members are electrically interconnected.

6. A cathode-ray tube as set forth in claim 1 wherein the rigid, conductive members are electrically separated from one another.

References Cited in the file of this patent UNITED STATES PATENTS 2,692,532 Lawrence Oct. 26, 1954 

